Blue duck. Whio. ( (Hymenolaimus malacorhynchos)
The blue duck or whio is an iconic species of clear fast-flowing rivers, now mostly confined to high altitude segments of rivers in North and South Island mountain regions. Nowhere common, it lives at low densities and its shrill “whio” whistle above the noise of turbulent waters will usher in a long-remembered encounter...Adults of both sexes are alike, being uniformly slate blue-grey with chestnut spotting on the breast, a pale grey bill with a conspicuously expanded black flap at its tip, dark grey legs and feet, and yellow eyes. During aggressive interactions, or when birds are suddenly frightened, the bill epithelium is flushed with blood, and appears distinctly pink. Males are larger than females, have more breast spotting and more prominent greenish iridescence on the head, neck and back. Immatures are similar to the adults but from late summer to about August their eye is dark, their bill a dark grey and their chest spotting sparse and dark.